http://arxiv.org/abs/2106.01928
We present a new set of index-based measurements of [$\alpha$/Fe] for a sample of 2093 galaxies in the SAMI Galaxy Survey. Following earlier work, we fit a global relation between [$\alpha$/Fe] and the galaxy velocity dispersion $\sigma$ for red sequence galaxies, [$\alpha$/Fe]=(0.378$\pm$0.009)log($\sigma$/100)+(0.155$\pm$0.003). We observe a correlation between the residuals and the local environmental surface density, whereas no such relation exists for blue cloud galaxies. Returning to the full sample, we find that galaxies in high-density environments are $\alpha$-enhanced by up to 0.06 dex at galaxy velocity dispersions $\sigma$<100 km/s, compared to their counterparts in low-density environments. This $\alpha$-enhancement includes a dependence on morphology, with an offset of 0.057$\pm$0.014 dex for ellipticals, and decreasing along the Hubble sequence towards spirals, with an offset of 0.019$\pm$0.014 dex. Conversely, for galaxies with $\sigma$>100 km/s in low-density environments, the [$\alpha$/Fe]-$\sigma$ relation is consistent across all morphological types earlier than Sc. At low galaxy velocity dispersion and controlling for morphology, we therefore estimate that star formation in galaxies in high-density environments is truncated $\sim$1 Gyr earlier, compared to those in low-density environments. At the highest velocity dispersions, $\sigma$>200 km/s, we find no difference in the [$\alpha$/Fe] ratio of galaxies earlier than Sc. Hence, we infer that the integrated star-formation timescales cannot differ substantially between high-$\sigma$ galaxies across varied environments, supporting the relative dominance of mass-based quenching mechanisms at the highest mass scales.
P. Watson, R. Davies, S. Brough, et. al.
Fri, 4 Jun 21
52/71
Comments: 15 pages, 9 figures
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